Can't keep fuel equal in tanks.

[DVT873]

If all of the FASS return was going to one tank that will be a problem. Interesting about the returns having standpipes. Mostly I see medium duty trucks, smaller tanks and those don't have standpipes. If they are on both sides and the same length it would be fine. These dual draw dual return systems can be a PIA when they act up.

A lot of newer stuff use a fuel pump to move fuel from the "storage tank" to the run tank. Pretty reliable but when they act up it can be a problem if somebody doesn't know the system. Hope splitting the FASS return fixes your problem.